Piercing process

ABSTRACT

An improvement in the piercing of difficult to pierce metal alloy billets where the billet is drilled throughout its axial length, a lubricating material such as glass inserted in the fore end of the bore of the billet, and the billet then heated to a working temperature. The hot billet is readily pierced with the lubricant facilitating in the piercing process.

United States Patent [191 Ca'uley et al.

[ June 25, 1974 PIERCING PROCESS [75] Inventors: William J. Cauley,Beaver Falls;

Joseph F. Maykuth, Aliquippa, both of Pa.

[73] Assignee: The Babcock & Wilcox Company, New York, NY.

[22] Filed: July 17, 1972 [21] Appl. No.: 272,614

[52] US. Cl. 72/41, 72/209 [51] Int. Cl B21b 17/10 [58] Field of Search72/41, 42, 46, 209

[56] References Cited I UNlTED STATES PATENTS 1 2,630,220 3/1953Sejournet 72/42 2,791,924 5/1957 Sawyer .Q. 72/42 2,956,337 10/1960Buffet et al. 72/41 3,335,589 8/1967 Buffet 72/4l FOREIGN PATENTS ORAPPLICATIONS 2,007,250 9/1970 Germany 72/42 Primary Examiner-Charles W.Lanham Assistant Examiner-E. M. Combs [5 7] ABSTRACT An improvement inthe piercing of difficult to pierce metal alloy billets where the billetis drilled throughout its axial length, a lubricating material such asglass inserted in the fore end of the bore of the billet, and the billetthen heated to a working temperature. The hot billet is readily piercedwith the lubricant facilitating in the piercing process.

4 Claims, 6 Drawing Figures 1 PIERCING PROCESS The present inventionrelates to improvements in rotary piercing processes and the like andmore particularly to the rotary piercing of hot billets of stainlesssteel alloys and other metals and metal alloys difficult to pierce, inthe manufacture of seamless hollows or tubes.

All commercial rotary piercing processes have the common feature of theformation of a hollow by peripherally rolling a hot cylindrical billetover a conical mandrel by driven rolls set at an angle to the horizontalplane through the center line of the piercing mill. The action' of thepiercer rolls or cones consists of gripping the hot billet, advancing itby reason of the skew rolling action imparted by the feed angle of theroll axes, reducing the diameter of the billet, and then helicallyrolling the reduced billet over the conical mandrel between the drivenrolls and offset guide rolls.

The rotary piercing of high alloy steels of the stainless type, evenwhen the alloy constituents have been balanced in an effort to stabilizethe phase of the alloy and effect improvement in high temperatureductility, has proved to be much more difficult than piercing billets ofcarbon steels. A suitable metal ductility when hot is necessary towithstand the various tensional, compressional, and torsional forces setup in piercing. The deformation of the metal in rotary piercing involvesperipheral skew rolling which is largely compressive in nature, areduction in wall thickness, a bending action on the outermost andinnermost surfaces of the hollow, an abrading action on the inner andouter surfaces of the hollow caused by differences in the relativesurface speeds of the hollow, mandrel and the driven and guide rolls,and a twisting action caused by the differential peripheral speeds ofthe hollow and the rolls at various points in the pass. A high degree ofcare must be exercised in such cases to provide the proper roll feedangle, suitable speeds of the piercer rolls, and a careful location ofthe piercing point to minimize internal marking of the pierced hollow.To secure the proper relative positions of the piercing point andbillet, it is now customary to provide by drilling, burning or punchinga center recess or starting hole in the billet end in which the piercingpoint is centered at the start of the piercing operation.

Even when the piercing point is made of a metal or metal alloy which hasthe desired qualities of toughness and wear resistance at hightemperatures, and which does not spall or crack at the surface when theworking layer is heated to a high temperature while the body remains ata much lower temperature, it has been found with billets of thecharacter described, that the internal surface of the pierced hollow hasbeen marked or fissured to an extent requiring a further conditioningoperation to secure the desired inside finish before repiercing ordrawing the pierced hollow. Efforts have heretofore been made tolubricate the piercing point to lengthen the working life of the point,and also to improve the internal surface condition of the hollow.

An effective means for lubricating the piercing operation was disclosedin the Sawyer US. Pat. No. 2,791,924 wherein ordinary bottle glass insolid or fiber form was inserted in the facing end of a hot billetimmediately prior to the hot piercing of the billet. This processhowever has certain practical drawbacks both from a mechanical andprocess standpoint. Due to manipulative problems in handling a hotbillet, it has been found difficult to properly insert the lubricatingmaterial in the end of the hot billet and to maintain the material inposition during the piercing operation. Sometimes the lubricatingmaterial will be exuded outwardly of the billet during initial piercingpoint operation leaving insufficient material for effective lubricationof the outward end of the billet. This is particularly true whenpiercing longer billets which is the modern procedure, where billets aretwice as long as those handled 15 to 20 years ago.

In the present invention we have overcome the above difficulties ofproviding adequate and reliable lubrication during the piercing process.This is accomplished by drilling the billet throughout its length andinserting the lubricating material in the billet prior to heating thebillet to its working temperature. The lubricating material may be inany suitable form, however we have found it convenient to use rods orbars of sintered window glass and to fix the rods in the fore end of thebore by fiber glass. Since in the usual course of events the billetswill be subjected to acertain amount of handling by cranes and the likethe lubricating material must be securely placed in the bore of thebillet to withstand such handling particularly before the billet isheated. Heating the billet to a working temperature will increase theintegrity of the lubricant material in the bore due to a limited meltingof the glass and adhesion to the metal of the billet. Of the drawings:

FIG. 1 is a diagrammatic illustration of a cone-type piercing mill, towhich the operation of the invention is applicable;

FIG. 2 is a vertical section through the fore end portion of a billetwith the lubricating material in position;

FIG. 3 is an end view of the billet shown in FIG. 2;

FIG. 4 is a section view of a billet with lubricating materialpositioned therein;

FIG. 5 is a section of a billet taken on line 5+5 of FIG. 4; and

FIG.'6 is a perspective view of a glass rod prior to insertion in thebillet.

While the present invention is also adapted for use in other commercialtypes of piercing mills, such as the Mannesmann or parallel axis barreltype roll piercing mill or the Stiefel or 180 disc mill, it has beenillustrated as applied to a 60 cone roll piercing mill in which a solidbillet 10 is rotated and advanced by a pair of angularly arrangeddiametrically opposite rolls l2 rotated in the directions indicated bythe arrows in FIG. 1 to cause the rotating billet to flow over and abouta conical piercing point 14 mounted on a bar 16. The piercing point isheld against longitudinal movement but is free to rotate with the billetbeing pierced.

In the invention procedure the workpiece or billet 10 will usually becylindrical, and a typical size will be 5 to 8 inches in diameter and toinches long. The billet will be center drilled along the longitudinalaxis to a bore 18 diameter of about 1 inch. The billet will then becounterbored on one end to form a conical opening 20 of about 2% inchbase merging into the 1 inch bore. Extending the bore throughout thelength of the billet will aid in maintaining reasonable concentricity ofthe pierced workpiece with a reasonable uniformity of pierced billetwall thickness.

After the billet has been bored, the lubricant will be inserted in thebore 18 adjacent the conical end 20. The lubricant advantageously willbe a glass, such as window glass, which may be powdered, solid orfibrous. We have found that sintered glass particles formed as 10 inchlong half round rods 22 with a A inch diameter are convenient for thepurpose, see FIG. 6. The rods of semi-circular cross-section areinserted in the bore 18 in end adjoining pairs and packed in glass fiber24 to retain their positioned relationship in the bore of the billet.Thus in all sizes mentioned, the 20 inches of glass material, positionedadjacent the enlarged or conical end 20 of the billet 10 will providesufficient lubrication for billet piercing without appreciably exceedinglubrication requirements. lt will be understood that excessive amountsof lubricant can lead to piercing difficulties where glass may depositon the rollers 12 causing slippage and incomplete piercing operations.

With the lubricant positioned as described, the billet 10 will bepositioned in the furnace for heating to proper working temperatures. Inthe usual billet heating furnace the billets are maintained in ahorizontal position throughout the heating cycle and the softening ofthe glass lubricant such as the rods 22 and fiber 24 will tend toincrease the positional stability of the glass in the bore 18. As thebillets, at the desired temperature are moved from the furnace to thepiercing rolls, the billet will normally be maintained in a generallyhorizontal position so that the glass lubricant will be retained at itsproper location in the bore. Ordinary tilting of the hot billet 10 orjolting during billet transfer has not adversely influenced thepositional stability of the glass lubricant therein.

With the lubricating glass in a viscous condition, the insertion of theconical piercing point 14 into the conical opening 20 of the hot billet10 will contact a film of glass and will continue to be in lubricatingcontact with the glass as the billet is forced thereover in the piercingprocess. We have found it advantageous during the initial installationof the lubricant in a cold billet, heating the billet with the lubricanttherein and during the piercing operation to use the described sinteredglass rods 22 with the fiber glass packing 24. The rods are initiallyformed from crushed window glass of 50 mesh size, placed in a mold andheated in a low temperature oven at 800 to 1,000F. The rod so producedwill have a rough surface and will have sufficient strength forreasonable handling and placement in the billet. During heating of thebillet with the glass therein, the material will adhere to the surfaceof the billet bore 18 and will thus provide a reservoir of lubricantwhich will be distributed during the piercing operation. The resultantpierced billet will have a clean smooth inner surface with a relativelylow expenditure of piercing energy. Little, if any, surface conditioningof the pierced product will be necessary prior to the conversion of thepierced billet into a saleable tubular product.

What is claimed is:

l. The method of rotary piercing a hot metal workpiece of circularcross-section having a center bore extending axially through the lengththereof which comprises, placing in the center opening of the workpiecea body of incombustible lubricating material having a relatively widerange of fusion temperatures below the workpiece hot workingtemperature, heating the workpiece material therein; rotating about asubstantially horizontal axis and axially advancing the workpiece whileat the predetermined hot working temperature by a skew rolling actionrelative to a conical piercing point with the point horizontally alignedwith the center opening and the lubricating material generallysymmetrically arranged in the center opening relative to the piercingpoint, and piercing the workpiece at such a rate the lubricatingmaterial contacting with the hot workpiece progressively fuses and formsan outer layer of fused lubricating material and a continuously thinninginner layer of relatively solid lubricating material only between theworking surface of the piercing point and the portions of the workpiececontacting therewith.

2. The method of claim 1, wherein the lubricating material is glass.

3. The method of claim 2 wherein the glass comprises sintered granularwindow glass.

4. The method of claim 1 wherein the lubricating material comprisessintered glass rods retained in the bore of the billet by fiber glass.

1. The method of rotary piercing a hot metal workpiece of circularcross-section having a center bore extending axially through the lengththereof which comprises, placing in the center opening of the workpiecea body of incombustible lubricating material having a relatively widerange of fusion temperatures below the workpiece hot workingtemperature, heating the workpiece material therein; rotating about asubstantially horizontal axis and axially advancing the workpiece whileat the predetermined hot working temperature by a skew rolling actionrelative to a conical piercing point with the point horizontally alignedwith the center opening and the lubricating material generallysymmetrically arranged in the center opening relative to the piercingpoint, and piercing the workpiece at such a rate the lubricatingmaterial contacting with the hot workpiece progressively fuses and formsan outer layer of fused lubricating material and a continuously thinninginner layer of relatively solid lubricating material only between theworking surface of the piercing point and the portions of the workpiececontacting therewith.
 2. The method of claim 1, wherein the lubricatingmaterial is glass.
 3. The method of claim 2 wherein the glass comprisessintered granular window glass.
 4. The method of claim 1 wherein thelubricating material comprises sintered glass rods retained in the boreof the billet by fiber glass.